Phase I/II, Two-Part, Multicenter First-in-Human Study of Ifinatamab Deruxtecan (DS-7300a, I-DXd) in Subjects With Advanced Solid Malignant Tumors (IDeate-PanTumor01)

Inclusion Criteria: * Eastern Cooperative Oncology Group (ECOG) Performance Status score of 0 or 1. * Has at least 1 measurable lesion according to Response Evaluation Criteria in Solid Tumors (RECIST) Version 1.1 on computed tomography (CT) or magnetic resonance imaging (MRI) as assessed by Investigator. Measurable lesions should not be from a previously irradiated site. If the lesion at a previously irradiated site is the only selectable target lesion, a radiological assessment showing significant progression of the irradiated lesion should be provided by the Investigator * Has adequate cardiac, hematopoietic, renal and hepatic functions * Has an adequate treatment washout period prior to start of study treatment * Has a pathologically documented advanced/unresectable or metastatic head and neck squamous cell carcinoma, esophageal squamous cell carcinoma, squamous and adenocarcinoma non-small cell lung cancer (NSCLC), small cell lung cancer (SCLC), bladder cancer, sarcoma, endometrial cancer, melanoma, adenocarcinoma CRPC (primary neuroendocrine or histologically confirmed neuroendocrine differentiated prostate cancer is not allowed), breast cancer that is refractory to or intolerable with standard treatment, or for which no standard treatment is available. For Expansion Cohort 4 2L ESCC participants only: * Has disease progression a post platinum-based and an immune checkpoint inhibitor (ICI) treatment per global or local guidelines, with a maximum of one prior line of systemic therapy for unresectable advanced or metastatic ESCC. Exclusion Criteria: * Has prior treatment with B7-H3 targeted agent, including I-DXd. * Has had prior discontinuation of an antibody drug conjugate (ADC) that consists of an exatecan derivative (e.g., trastuzumab deruxtecan) due to treatment-related toxicities. * Has multiple primary malignancies within 3 years, except adequately resected non-melanoma skin cancer, curatively treated in situ disease, superficial GI tract tumors and non-muscle invasive bladder cancer curatively resected by endoscopic surgery. * Uncontrolled significant cardiovascular disease * Clinically severe pulmonary compromise resulting from intercurrent pulmonary illnesses including, but not limited to, any underlying pulmonary disorder, or any autoimmune, connective tissue or inflammatory disorders with potential pulmonary involvement, prior pneumonectomy, or requirement for supplemental oxygen * Has an uncontrolled infection requiring systemic therapy. * Has substance abuse or any other medical conditions that would increase the safety risk to the subject or interfere with participation of the subject or evaluation of the clinical study in the opinion of the Investigator.